Automatic Identification, or Auto-ID, is a term given to a broad category of technologies for the reliable and efficient identification, location, and tracking of objects. Two examples of Auto-ID technologies are bar coding and Radio Frequency Identification (RFID).
With bar coding a reading device uses optical laser or other imaging technology to scan and interpret a printed barcode on a label that is affixed to a respective object. However, with RFID, a reading device (or, reader) receives and interprets radio frequency electromagnetic signals transmitted wirelessly by a small electronic RFID tag that has been affixed to, or is otherwise associated with, a respective object. In a similar manner to bar coding, each RFID tag may transmit a unique radio frequency signal so as to uniquely identify the object with which it is associated. Alternatively, in a particular application, multiple RFID tags may transmit the same radio frequency signal if such uniqueness is not required.
An RFID tag is typically a radiofrequency transponder comprising a radiofrequency signal receiver and a radiofrequency signal transmitter in a single package, along with some processing circuitry to trigger transmission of the RFID tag's radiofrequency signal upon reception of an exciter signal (or, interrogation signal). Depending upon the needs of a particular application, an exciter signal may be transmitted from the same physical device as the reader, or by a separate device. An active RFID tag further includes a power source such as a battery for powering its own reception and transmission, whereas a passive RFID tag does not include its own such power source and is instead powered by electromagnetic energy in the exciter signals. Hybrid RFID tags exist that include a battery for supplementing the energy received in the exciter signal.
It is known for an RFID tag to be designed to derive the radiofrequency signal it transmits from the exciter signal it receives, whether using the same or a multiple of the carrier frequency of the exciter signal, or the same unique information carried in an exciter signal, for some examples. With an RFID tag using modulated backscatter, the exciter signal received at the RFID tag's antenna produces an electronic signal that can itself be modulated by the tag's processing circuitry with a unique signal stored on the tag, and routed back to the same antenna for transmission. In this sense the exciter signal received at the RFID tag is modified and “reflected” back to the exciter. With such an RFID tag, receiving and transmitting may be carried out by the same antenna and an entirely separate transmitter circuit is not required. It is also known for an RFID tag to be designed to transmit radiofrequency signals that are independent in that they are not so derived from a received exciter signal. As would be understood, the type of RFID tag chosen for a particular application depends on the needs of the application, the associated costs, and other factors.
The RFID reader/exciter may use a gated antenna array that includes a pair of vertically mounted antennae. The vertically mounted antennae are caused by suitable electronic circuitry to each produce and emit an electromagnetic exciter signal, as a respective interrogation field, at a particular frequency. The interrogation fields together form an interrogation zone in which the RFID device can be interrogated (i.e. excited) and detected. If an RFID tag is positioned within the interrogation zone for a sufficient time and is able to receive appropriate commands from the reader/exciter as well as adequate RF power to operate the device, it will become stimulated and transmit, either by generation of a radio frequency signal or by reflective means (i.e., using modulated backscatter), a uniquely coded signal that can be received by the same reader/exciter antennae that transmitted the exciter signal, or by a separate receiving antenna. The response signal from the RFID tag can be read by the reader, typically with a readable range on the order of a few feet, though broader or narrower ranges are possible.
A common application for RFID systems is in tracking objects for shipping such as shipping containers in a shipping terminal, or for waste management such as waste containers within a waste management facility. In such applications, the RFID tags are placed on the containers and are interrogated by RFID readers located at various locations within the terminal or facility, including vehicles, cranes, or other container moving equipment. In a waste management application, the event of a fork truck or front loader garbage truck picking up a waste container may need to be registered as an event for tracking the progress of waste management. In this process it may be useful to determine or validate the presence of the container on the end of the forks or other container lift mechanism and determine that the container was lifted to a particular height on its way to a dumping position. However, where registering this event requires the excitation and reception of radiofrequency signals from RFID tags affixed to the waste container, often there is a failure to register the event due to inadvertent shielding of radio signals resulting from radio frequency (RF) blocking materials (such as metal or liquids), interference between transmissions of multiple RFID tags in the vicinity, distance between RFID tags and readers, and other factors.
Another problem with an RFID tag placed on a container (a problem shared with bar coding) is that the container must always be aligned or picked up from the side of the container on which the RFID tag is mounted in order to be in the field of view of the barcode reader or RFID reader. As this is not always possible, nor practical, it is known to place each of multiple RFID tags at respective different locations on the container to improve the chances of reading by respective readers. It has been observed that this approach demands constant inspection, testing, and maintenance of the RFID tags to ensure that they remain operable and are positioned so as to be readable. This of course leads to increased operating costs and resources.
Some prior art systems determine the presence of a bin on the forks using proximity sensors and weight sensors mounted on the forks to detect the difference in load resistance during movement of the arms. Other systems determine a lift action using a sensor for detecting when the forks are in the up position as compared with a down position. However, such sensing equipment requires external wiring to connect the sensing equipment to other parts of the system, and the wiring itself is subject to mechanical failure, sensitive to rain, snow, heat in the environment and accordingly often requires regular servicing. In systems using proximity sensors, the proximity sensors themselves are generally exposed to the elements as they are generally mounted outside the vehicle. It has been observed that performance of such proximity sensors can be impaired when the sensors and/or wiring is/are covered with snow or ice. For example, false triggers are prevalent. In systems that detect presence of containers using the weight differential between unloaded forks and loaded forks, sensors or strain gages may be affixed directly on the forks. Alternatively, weight differential may be detected by detecting pressure differentials in hydraulic fluid in the hydraulic lifting equipment with and without a load on the lifting mechanism. However, these kinds of sensors are complex, typically require external mounting and wiring of sensitive components, typically require very tight integration with subcomponents of the vehicle itself, and typically require onerous maintenance and calibration.